Initiator Integrated Poly (Dimethylsiloxane) and Methods for Making the Same and Its Application

ABSTRACT

Disclosed herein is an initiator integrated polydimethylsiloxane (iPDMS). The iPDMS is a polydimethylsiloxane undergoing a hydrosilylation reaction. The initiator 10-undecenyl 2-bromo-2-methyl propionate is integrated on the surface of iPDMS by covalent bond. At % is 0.01-1% confirmed by X-ray photoelectron spectroscopy. Disclosed herein is a method for making an initiator integrated polydimethylsiloxane. Prepolymer A, cross-linker B and vinyl-terminated initiator C were mixed below a ratio of 10:1:4-0.01 for 6-24 hours, then the elastomer was formed. And, disclosed herein is functional surface modification of initiator integrated polydimethylsiloxane and its applications for biocompatibility, organic solvent compatibility and heat-sensitive materials.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a continuation of U.S. patent application Ser. No.12/531,484 filed Feb. 25, 2010, which is a national stage application ofInternational Application No. PCT/CN2008/000494, filed on Mar. 13, 2008,which claims priority to Chinese Application No. 200710064501.6, filedMar. 16, 2007, which applications are incorporated herein in theirentirety by this reference.

FIELD

This invention belongs to the field of materials. Disclosed herein is aninitiator integrated poly (dimethylsiloxane) and methods for preparingthe same. Also disclosed herein is modifying the initiator integratedpoly (dimethylsiloxane) and applications of the modified initiatorintegrated Polydimethylsiloxane for biocompatibility, organic solventcompatibility and heat-sensitive materials.

BACKGROUND

Poly (dimethylsiloxane)(PDMS) is the first choice of material for a widerange of applications like microfluidic system, micro-electromechanicalsystem, soft lithography and unconventional nanolithography, becausePDMS has many advantageous properties such as nontoxicity, transparency,flexibility and chemical inertness. Furthermore, PDMS is widely used inmany industrial areas such as aviation, electric, medical apparatus.Surface modification of PDMS is needed in order to play the bestfeatures of PDMS based devices and further promote the application ofPDMS. A number of strategies have been developed for PDMS surfacemodification, which can be divided into two categories, namelyphysisorption and chemical coupling.

Physisorption of materials to PDMS surface, such as surfactants andpolyelectrolytes are driven by hydrophobic force and electrostaticforce, respectively. Although this method is simple, the surface filmobtained is less stable and affected by the environmental changes suchas temperature and pH change. And, the value of the density andthickness for the surface film are low, and limited to 4 gcm⁻² and therange of 1 to 5 nm, so that it could be only applied to the verycomplicated environment such as the diluted serum, the pretreated thecell broken solution etc., or be used in the condition of relativestable environment and low shear force.

Chemical coupling can radically overcome the defect that the filmabsorbed by physisorption is unstable and is stable but is difficult toachieve because PDMS is chemically inert, which is ironically one of itsmerits. Common for this method, published in the literature: Dozel, C.;.Geissler, M.; Bernard, A.; Wolf, H.; Michel B.; Hilborn, J.; Delamarche,E. Adv. Mater. 2001,13,1164, the first step is to apply high-energybombardment (i.e., plasma) to PDMS surface, which results in a silicatelayer with functional groups on the surface, such as —OH, —COOH, and—NH₂. Those functional groups not only render the surface hydrophilicitybut also allow further modification via chemical coupling. Chemicalcoupling has two problems: (1) Plasma treatment is easy but notsustainable; recovery of hydrophobicity of treated. PDMS is welldocumented. High-energy bombardment also has the tendency to damagePDMS. Furthermore, this strategy is only applicable to planar structurebecause of its limited penetration depth. (2) Concentration gradient in“grafting to” strategy prevents the preparation of thick and densefilms.

Traditional physisorption and chemical coupling cannot satisfy with therequirement of PDMS. Another method, designing and composing newmaterials, is advanced by the researchers. New materials have beendeveloped to replace PDMS. For example, a photocurableperfluoropolyether(PEPEs) was synthesized to fabricate microfludicdevices that were organic solvent compatible. This material waspublished in the literature: J. P. Rolland, R. M. Van Dam, D. A.Schorzman, S. R. Quake, J. M. DeSimone, J. Am. Chem. Soc. 2004, 126,2322. However, this method needs researchers develop a new material forevery application. In a consensus, it is costly to develop a newelastomer for each individual need. Development ofMicro-electromechanical system (MEMS) is a main direction of applicationof PDMS. Improving the biocompatibility of PDMS has been a hotspot.However, the material which meets the main property (mechanicalproperty) and surface property (biocompatibility) to replace PDMS hasnot been reported up to now. Surface modification is an important factorto impact the application of materials and the performance. It canintroduce new surface properties as necessary and retain the excellentperformance of the main materials at the same time. And it is a highefficient and low consumed solution.

SUMMARY

Disclosed herein is aimed at overcoming the various defects in theconventional technology of modification of PDMS. Firstly, the presentinvention provides an initiator integrated poly(dimethylsiloxane). Thena functional groups are modified on the surface of initiator integratedpoly(dimethylsiloxane) through the surface-initiated polymerization. Themethod disclosed herein can be easy to achieve the universal, permanent,diversity and functional surface modification of poly(dimethylsiloxane).

The purpose of the invention is accomplished through the followingtechnical solution:

Disclosed herein is an initiator integrated poly(dimethylsiloxane)(iPDMS). The iPDMS is a poly(dimethylsiloxane) undergoing ahydrosilylation reaction. 10-undecenyl 2-bromo-2-methyl propionate isintegrated on the surface of iPDMS through covalent bond. And, atomicconcentration (At %) is 0.01-1% confirmed by X-ray photoelectronspectroscopy (XPS).

Disclosed herein is a method for preparing an initiator integratedpoly(dimethylsiloxane) including mixing prepolymer A, cross-linker B andvinyl-terminated initiator C below a weight ratio of 10:1:4-0.01 for6-24 hours and then forming the elastomer, the initiator integratedPolydimethylsiloxane of the present invention.

The said prepolymer A is poly(dimethyl-methylvinylsiloxane).

The said cross-linker B is vinyl-endcappedpoly(dimethyl-methylvinylsiloxane) orpoly(dimethyl-methylhydrogenosiloxane).

The said vinyl-terminated initiator C is 10-undecenyl2-bromo-2-methylpropionate.

The functional groups are modified on the surface of iPDMS of thepresent invention through the surface-initiated polymerization forbiocompatibility, organic solvent compatibility and heat-sensitivematerials. The film (the thickness of the film>50 nm) can prevent theabsorption of the protein in case of carrying out SI-ATRP ofoligo(ethylene glycol) methyl methacrylate from iPDMS for permanent andfunctional surface coating. The film can prevent the infiltration ofCH₂Cl₂ in case of carrying out SI-ATRP of 1H, 1H, 2H, 2H-perfluorodecylmethacrylate(FMA) from iPDMS for permanent and functional surfacecoating. And, the film can quickly change between hydrophobic (>32° C.)and hydrophilic (<32° C.) in case of carrying out SI-ATRP ofpoly(N-isopropylacrylamide) from iPDMS for permanent and functionalsurface coating.

According to the present invention, a vinyl-terminated initiator C wasmixed with prepolymer A and cross-linker B, and absorbed covalentlyhighly cross-linked with three-dimensional networks of PDMS throughhydrosilylation reaction as showed in the FIG. 1, resulting in aninitiator integrated PDMS. The initiator is distributed on the surfaceof this initiator integrated PDMS in the atomic concentration of0.01-1%. And then we carried out SI-ATRP from iPDMS for permanent andfunctional surface coating. The material is used to preparethree-dimensional materials and apparatus, such as functional surfacemodification PDMS for microfluidic system, micro-electromechanicalsystem, soft lithography and unconventional nanolithography.

The present invention provides a facile method for permanent andfunctional surface modification of PDMS based on a commercial material.As compared with physisorption, an initiator was integrated by covalentbond firstly. Then a functional molecule was integrated with initiatorby chemical bond. Therefore, the method of the present avoids theunsteadiness of the surface prepared by physisorption. According to thetechnical solutions of the present invention, the density of thefunctional surface can be tuned by varying the content of initiator, andthe thickness of the functional surface can be tuned by selectingfunctional molecule.

As compared with chemical coupling, the method herein is very simple.And, the “functional” chemical groups on the surface of PDMS won'tvanish even though exposed to the air for a long time. iPDMS is the sameas PDMS in applications for replica molding, soft lithography, andmicro-electromechanical system. The method used for surface modificationvia SI-ATRP could be carried out in the assembled micro-channel, whichenables realizing the complex micro-system for high-performance surfacemodification.

DESCRIPTION OF DRAWINGS

FIG. 1 shows the reaction equation of the preparation of iPDMS.

FIG. 2 shows XPS of normal PDMS (the curve 1) and iPDMS prepared inexample 1 (the curve 2), wherein inserted was the amplified core scan ofBr 3d.

FIG. 3 shows XPS confirmed successful surface modification from iPDMSvia SI-ATRP: (A) survey scan of poly(FMA) coating in example 2, and (B)poly-(OEGMA) coating in example 3.

DESCRIPTION

The PDMS was purchased from Dow Corning. The initiator 10-undecenyl2-bromo-2-methylpropionate and monomers, oligo(ethylene glycol) methylmethacrylate, and 1H, 1H, 2H,2H-perfluorodecyl methacrylate werepurchased from HZDW (Hangzhou, China).

Example 1 Synthesis of iPDMS Having the Atomic Concentration of 1%

According to the method shown in FIG. 1, prepolymer A(poly(dimethyl-methylvinylsiloxane)), cross-linker B (vinyl-endcappedpoly(dimethyl-methylvinylsiloxane)) and vinyl-terminated initiator C(10-undecenyl 2-bromo-2-methylpropionate) were mixed below a ratio of10:1:4 for 24 hours and then the elastomer which is the initiatorintegrated poly(dimethylsiloxane) of the present invention was formed.X-ray photoelectron spectroscopy(XPS) was applied to characterize thesurface composition of iPDMS. The value of atom % is 1%. Compared withregular PDMS, initiators referred were presented at the surface of PDMSand its amount is enough to initiate the polymer reaction to accomplishthe surface modification of PDMS.

Example 2 SI-ATRP of oligo(ethylene glycol) methyl methacrylate fromiPDMS Prepared in the Example 1

We carried out SI-ATRP of oligo(ethylene glycol) methyl methacrylatefrom iPDMS for permanent and functional surface coating. iPDMS wasplaced in a 100 ml bottle and processed anaerobic treatment. Incompletereaction mixture (IRM) and complete reaction mixture (CRM) wereprepared: IRM was obtained by mixing well with water (5 mL), methanol(10 mL), and the monomer oligo(ethylene glycol) methyl methacrylate (8mmol, 0.35M); CRM was obtained by adding the catalyst, CuBr (36 mg, 0.25mmol) and bipyridine (78 mg, 0.5 mmol), to the IRM, resulting in adark-red solution. Both IRM and CRM were deoxygenated right before use.

The mixture was transferred into the bottle with iPDMS under inert gasprotection. Then reaction was continued for 24 hours at 20° C., followedby taking out iPDMS, rinsing it with methanol and Milli-Q water, dryingunder the flowing nitrogen, and obtaining the polymer film ofoligo(ethylene glycol) methyl methacrylate (the thickness>50 nm). ItsXPS was shown as FIG. 3A, in which the characteristic indicated thesignal of carbon was enhanced and silicon was weakened. Inserted werethe core scans of the characteristic carbon. The information clearlyindicated the success of polymerization and oligo(ethylene glycol)methyl methacrylate film deposition on the surface of iPDMS. The filmcan prevent the absorption of protein, which is prove by observing nofluorescence signal by the fluorescent microscope after immerging themodified iPDMS into Alex488-BSA. for 2 hours at 4° C. and rinsing withPBS buffer (Ph=7.4). Alex488-BSA was dissolved in PBS buffer (pH=7.4),and the concentration is 1 mg/ml.

Example 3 SI-ATRP of 1H, 1H, 2H, 2H-perfluorodecyl methacrylate(FMA)from iPDMS Prepared in the Example 1

We carried out SI-ATRP of 1H, 1H, 2H, 2H-perfluorodecylmethacrylate(FMA) from iPDMS for permanent and functional surfacecoating. iPDMS was placed in a 100 ml bottle and treated anaerobicly.Incomplete reaction mixture (IRM) and complete reaction mixture (CRM)were prepared, wherein IRM was obtained by mixing well withdichloromethane and the monomer 1H, 1H, 2H, 2H-perfluorodecylmethacrylate(FMA) (8 mmol, 0.35M); and CRM was obtained by adding thecatalyst, CuBr (36 mg, 0.25 mmol) and bipyridine (78 mg, 0.5 mmol), tothe IRM, resulting in a dark-red solution. Both of IRM and CRM weredeoxygenated right before using.

The mixture was transferred into the bottle with iPDMS under inert gasprotection. Then reaction was continued for 24 hours at 20′C, followedby taking out iPDMS, rinsing it with methanol and Milli-Q water, anddrying under the flowing nitrogen. In FIG. 3B, the characteristic F peakat 699 eV clearly indicated the success of polymerization and filmdeposition. The film can prevent the infiltration of CH₂Cl₂, which isproved by observing the modified iPDMS non-swelling after immerging itinto 10 ml dichloromethane for 2 hours at 20° C.

Example 4 SI-ATRP of poly(N-isopropylacrylamide) from iPDMS Prepared inthe Example 1

We carried out SI-ATRP of poly(N-isopropylacrylamide) from iPDMS forpermanent and functional surface coating. iPDMS was placed in a 100 mlbottle and treated anaerobicly. Incomplete reaction mixture (IRM) andcomplete reaction mixture (CRM) were prepared, wherein IRM was obtainedby mixing well with water (5 mL), methanol (10 mL), and monomerpoly(N-isopropylacrylamide)(8 mmol, 0.35M); and CRM was obtained byadding the catalyst, CuBr (36 mg, 0.25 mmol) and bipyridine (78 mg, 0.5mmol), to the IRM, resulting in a dark-red solution. Both of IRM and CRMwere deoxygenated right before using.

The mixture was transferred into the bottle with iPDMS under inert gasprotection. Then reaction was continued for 24 hours at 20° C., followedby taking out iPDMS, rinsing it with methanol and Milli-Q water, anddrying under the flowing nitrogen to obtain the film (the thickness>50nm). The film can quickly change between hydrophobic (>32° C.) andhydrophilic (<32° C.).

1. A method of making a polydimethylsiloxane carrying an initiator onits surface comprising the steps of: mixing prepolymer A, cross-linker Band vinyl-terminated initiator C with a weight ratio of 10:1:4-0.01causing a hydrosilylation reaction; keeping said mixture for 6-24 hoursto form polydimethylsiloxane carrying an initiator on its surface, whichresults from the hydrosilylation reaction, wherein said prepolymer A ispolydimethyl-methylvinylsiloxane, said cross-linker B is vinyl-endcappedpolydimethyl-methylvinylsiloxane or,polydimethyl-methylhydrogenosiloxane, and said vinyl-terminatedinitiator C referred is 10-undecenyl 2-bromo-2-methylpropionate.
 2. Afunctional polydimethylsiloxane which is obtained by carrying outSi-Atom Transfer Radical Polymerization of oligo(ethylene glycol) methylmethacrylate, 1H, 1H, 2H,2H-perfluorodecyl methacrylate, orN-isopropylacrylamide from iPDMS, wherein iPDMS results from ahydrosilylation reaction, with 10-undecenyl 2-bromo-2-methyl propionatein 0.01-1At % being fixed on its surface through covalent bond.
 3. Afunctional polydimethylsiloxane which is obtained by carrying outSI-ATRP of 1H, 1H, 2H, 2H-perfluorodecyl methacrylate from iPDMS,wherein iPDMS results from a hydrosilylation reaction, with 10-undecenyl2-bromo-2-methyl propionate in 0.01-1 At % being fixed on its surfacethrough covalent bond.
 4. A functional polydimethylsiloxane which isobtained by carrying out SI-ATRP of poly(N-isopropylacrylamide) fromiPDMS, wherein iPDMS results from a hydrosilylation reaction, with10-undecenyl 2-bromo-2-methyl propionate in 0.01-1 At % being fixed onits surface through covalent bond.